This invention relates generally to a system for reclaiming foundry sand. It is directed specifically to the reclaiming of sand used in a foundry in combination with sodium silicate binders.
Binders, such as sodium silicate (water glass), are used in foundry molds and cores to impart desirable strength and surface characteristics in sand casting processes. Use of sodium silicate binders allows a foundry to obtain closer tolerances in sand castings. The relatively high strength of the molds allows them to be used without back-up aids, such as jackets, flasks, and bottoms. Sodium silicate-sand mixtures strengthened by carbon dioxide are used widely for cores, because the cores can be quickly made and are ready to use without baking. Expendable cores used in permanent mold casting are commonly made by the sodium silicate-carbon dioxide process because of the dimensional accuracy obtainable. The process is suitable for all common castings alloys, including aluminum and magnesium. It is most widely used, however, for casting of steel, cast iron and copper alloys.
After use, the chunks of sand and sodium silicate binder are often discarded. Conventional wet sand-reclamation systems are expensive and somewhat inefficient. They often are not economically practical except in areas where the freight cost of new sand overshadows the cost of reclaiming used sand. Only relatively small percentages of reclaimed sand can be used, requiring substantial addition of new sand for reuse.
The purpose of this disclosure is to introduce a system for reclaiming used foundry sand containing sodium silicate binders in a continuous economical process which makes possible wide-scale usage of sodium silicate binders for general foundry use. Such usage will permit a foundry to capitalize on the dimensional stability of the sand-binder mixture now felt justifiable only for more precise casting requirements and for cores.
The system comprises a new process for handling the used sand during reclamation and new equipment used in that process.
For a general discussion of present foundry practice relating to sand molding, see Metals Handbook, 8th edition (1970) Volume 5 (Forging and Casting), published by the American Society for Metals, Metals Park, Ohio, pages 155-180. A discussion of the use of the sodium silicate binders in specific molding processes can be found in this publication at pages 203-208. Production of sand cores is described in the publication at pages 209-221. These portions of the publication are considered to constitute an examplary discussion of the state-of-the-art relating to utilization and reclamation of foundry sand including sodium silicate binders, and are hereby incorporated by reference in this specification.